Radio frequency (RF) devices often include integrated circuits (ICs) that operate to receive RF input signals, transmit RF output signals, or both receive and transmit RF signals. Where receive functionality is included, RF communication ICs typically convert analog RF input signals to digital samples and then perform digital processing on these digital samples. Where transmit functionality is included, RF communication ICs typically apply digital logic to process digital data and then convert this digital data to RF output signals that are transmitted from the RF communication IC. The digital data can be generated internally within the RF communication IC and/or can be based upon off-chip sources. For example, an RF communication IC can monitor analog inputs and sample those inputs with analog-to-digital converter (ADC) circuitry to convert analog signals to digital samples. Analog signals can include, for example, analog inputs from one or more sensor devices.
Different clocks are typically used within RF communication ICs for various purposes. For example, as part of the processing of RF input signals and/or RF output signals, a local oscillator (LO) clock is often generated and used to downconvert RF input signals to lower frequencies or to upconvert output digital data to RF output signals. In addition, as part of the digital operations within the RF communication IC, clocks are utilized to time digital switching circuitry within digital processors, ADC circuitry, digital logic, and/or other digital circuitry. Periodic current pulses associated with digital switching within the digital circuitry, however, can generate spurs that interfere with the RF signals or other operations for the RF communication IC.
For certain solutions, RF communication ICs also include digital circuitry that drives output pads with pulsed digital signals, such as PWM (pulse width modulation) output signals. This output circuitry, such as PWM circuitry, is often required to run at an internal frequency that is higher than the RF operational frequencies for the RF communication IC in order to provide high resolution pulse output signals. In addition, these solutions can also include analog-to-digital converter (ADC) circuitry that periodically samples analog input signals. Such systems often have the output (e.g., PWM) circuitry share the same clock source with the ADC circuitry or can also have logic circuitry associated with the output circuitry directly trigger the ADC circuitry to take samples of analog inputs at known times. For example, sampling by ADC circuitry can be triggered when the output of the PWM circuitry is stable and temporally far away from a toggle event for the PWM circuitry in order to reduce interference and improve the fidelity of digital samples generated by the ADC circuitry.
With regard to RF operations, pulse output signals for output circuitry of the RF communication IC can cause spurs that introduce large amounts of interference on the RF receive signals and/or RF transmit signals. For example, toggling an output pin, such as a GPIO (general purpose input/output) pin, based upon output signals from PWM circuitry can generate spurs that interfere with the RF receive signals and/or RF transmit signals.
Spurs and digital switching interference can be addressed by driving the digital circuitry within the RF communication IC, such as the ADC circuitry and the PWM circuitry, with a digital clock that is retimed off of the LO clock used by the RF circuitry to receive and/or to transmit RF signals. However, while this retimed digital clock reduces interference with respect to the RF input/output signals due to being based upon the LO clock used for RF receive/transmit, this retimed digital clock introduces jitter with respect to timing operations for the digital circuitry within the system. This jitter often degrades performance. For example, jitter introduced by the retimed digital clock can reduce fidelity of digital samples generated by the ADC circuitry from analog input signals. Thus, while LO-based retiming of clocks can improve performance of the RF circuitry by reducing interference from toggling output signals (e.g., as produced by PWM circuitry), this LO-based retiming also tends to degrade precision and accuracy of other digital circuitry within the RF communication IC such as ADC circuitry.